This invention relates to railroads particularly to methods of sorting cars in railroad yards.
The purpose of sorting railroad cars is to collect them into xe2x80x9cblocksxe2x80x9d or groups of cars moving together to the next rail terminal, or having commodity, car type or some other attribute in common. Once individual cars have been collected into blocks, the blocks can be assembled into trains. If a train makes any intermediate stops? blocks are usually arranged in order of the sequence of stops, so all intermediate switching can be performed from the front (or occasionally the rear) of the train. Armstrong, J. H. (1998) in The Railroad: What It Is, What It Does: The Introduction to Railroading, 4th Edition. Simmons-Boardman Books, Omaha. Nebr. offers an excellent introductory text with a section on railroad terminal operations at pp. 197-211.
A railroad xe2x80x9chump yardxe2x80x9d utilizes a raised section of track, from which cars are individually cut off, and allowed to roll by gravity into their proper classification tracks. This contrasts with a xe2x80x9cflat yardxe2x80x9d where railcars are individually shoved into their proper tracks by switch engines. In single stage sorting, only one block is assigned to a track at any point in time. Multiple stage sorting builds more than one block on each track simultaneously. Beckmann, M. J., McGuire C. B. and Winsten C. B. (1956) in Studies in the Economics of Transportation. Oxford University Press, London, on pp. 127-171 describe in detail the differences between hump versus flat yards, as well as ways their use can be coordinated to minimize total switching and delay cost. Troup, K. F., ed. (1975) in Railroad Classification Yard Technology: An Introductory Analysis of Functions and Operations, Transportation Systems Center, Cambridge, Mass., (DOT-TSC-FRA-7519), NTIS #PB246724, hereinafter Troup (1975), developed a xe2x80x9cprimerxe2x80x9d on railroad yard operations. In general, hump yards are better suited for classification of railcars one-at-a-time, while flat yards may be more efficient for large blocks or xe2x80x9ccutsxe2x80x9d of cars which remain coupled together during the switching movement.
Very few hump yards have been built in recent years, as railroads have suffered the loss of a large portion of their traffic base to trucking competitors. The clear trend has been towards closing of hump yards rather than building new facilities; in some cases, portions of old facilities remain in use as flat switching yards, as in Russell, Ky., Dewitt, N.Y., and Enola, Pa.; in some cases former hump yards have been converted into intermodal facilities as happened to Norfolk Southern""s yards in Atlanta, Ga. and Rutherford, Pa.; sometimes land has been released for non-transportation use, as in Potomac Yard, Va., just a stone""s throw away from the U.S. Patent and Trademark Office in Crystal City. Many surviving facilities now operate at close to maximum throughput and under a state of chronic congestion, to the point that they often cannot even accept newly arriving trains, which have to be parked on the main line. Needless to say, this has an extreme adverse effect on railroad service reliability, which in turn has contributed to further loss of traffic to the trucking industry.
Although computers and new hardware have automated some previously manual processesxe2x80x94in particular, control of speed and routing of freely rolling railcars in hump yardsxe2x80x94the fundamental process of sorting cars and associated facility designs have changed very little since hump yards were first invented nearly a century ago. In the single-stage sorting approach commonly in use today, each block is assigned its own track. Each car must be sorted only once, but the maximum number of blocks built is limited to the number of tracks available. For example, a 50track yard could build a maximum of 50 blocks at one time using a single stage approach. Yards designed for single stage sorting need a large number of tracks, so they can build the maximum number of blocks possible. Since cars are sorted into many tracks, individual tracks can be short. Usually there are not enough tracks to build all needed blocks, so small blocks typically have only part-time availability in the yard.
By contrast, multiple stage sorting needs fewer tracks, but each car must be sorted more than once. For example, using the xe2x80x9cgeometricxe2x80x9d or xe2x80x9ctriangularxe2x80x9d sorting patterns (see FIGS. 1 and 2), four trains with a total of 29 or 26 blocks, respectively, can be built simultaneously using only four tracks. Yards designed for multiple stage sorting need only a few tracks, but since each track must hold several blocks at once, tracks should be long enough to hold an entire train. The requirement to process cars more than once also implies a need for a high capacity hump.
Multiple-stage sing is undeniably a more powerful approach, but in the United States the need to process cars more than once has been viewed as costly and inefficient, so it has not been commonly applied in practice. Indeed, facilities designed for single-stage sorting are not well suited for multi-stage sorting because of differences in the basic design parameters for each kind of yard. But as will be shown herein, in a properly designed facility multiple-stage sorting can be not only more powerful, but even more efficient than single stage sorting because the costly flat switching operation at the xe2x80x9ctrimxe2x80x9d end of the yard can be eliminated altogether.
A primary objective of this invention is to provide railroads a practical means to classify cars on a priority basis. While some cars don""t need to move on any particular schedule, other cars have strict delivery deadlines. Although it is always desirable to be able to increase train capacity to handle all traffic on a same-day basis, it is not always possible to increase capacity nor would it always be economical. So in the event an outbound train has more cars than it can carry, it is essential to make certain that any cars having no remaining slack time in their delivery commitments have first access to available train capacity.
But today, because of the severely limited capabilities of single stage sorting, cars are sorted by destination block only, and not by specific outbound train. The scheme is essentially first come first served rather than reflecting the priority of individual shipments. Some cars not needing to go may occupy space needed to accomodate higher priority shipments, resulting in unnecessary missed connections and service failures.
If airlines (like railroads) allowed passengers to board aircraft without regard to whether they held tickets for a flight, revenue management would be impossible. The implications for railroads should be clear: to take advantage of revenue management technology which has been successfully applied by many other industriesxe2x80x94including railroads"" direct competitor, the trucking industryxe2x80x94it is essential that classification yard performance be improved to the level where connections can be guaranteed to specific trains. Yet, even very recent published literature as in Gallagher, J. (1999) Reconsider This, Traffic World, Jul. 12, 1999 on pp. 32-33 still holds that xe2x80x9cyou can""t use data in real time to modify the way you handle individual cars. It""s impractical.xe2x80x9d
Traditionally, large hump yards are subdivided into three separate areas, with tracks dedicated to specific functions: (a) Inbound trains; arrive on the receiving tracks. Cars are inspected for mechanical defects and air brakes released so cars can roll free. (b) To classify an inbound train, a switch engine couples to the train in the receiving yard and then shoves cars to the hump, where they are uncoupled and individually roll into their proper classification tracks by gravity. (c) Once enough cars have been collected to run an outbound train, or the scheduled xe2x80x9cclose-outxe2x80x9d time arrives, blocks of cars are pulled from the xe2x80x9ctrimxe2x80x9d end of the yard (opposite the hump) by switch engines and moved into the departure tracks. There, air hoses are reconnected, air brakes charged and tested, and a final inspection of the train is made before departure. A typical single stage hump yard design with these three subyards is diagrammed in FIG. 5.
Small yards combine all these functions on the same tracks, so they can be more flexible than large facilities; but since small yards usually rely on flat switching, they are not as efficient as larger hump yards. Traditional single stage hump yard designs have the following shortcomings:
(a) A large number of tracks are required. For each track, switches and car retarder units (used for speed control) are required, which are expensive to build and maintain.
(b) As many classification tracks xe2x80x9cfan outxe2x80x9d from the hump, the outermost tracks have sharp curves, which can bind the wheels of cars causing them to stop short of their destinations. When this happens, collisions or derailments may occur; processing must be stopped and those cars pushed clear with switch engines. Because of these interruptions, frequent use of xe2x80x9couter tracksxe2x80x9d reduces the productivity of the humping operation.
(c) Contrary to popular notion, each car must be handled at least twice in a single stage yard: first when the car is classified at the hump, then again in a flat switching movement when cars are pulled out of the trim end of the yard and moved to the departure yard.
(d) If a needed block has only a part-time assignment, and if that block is not allocated in the classification yard when cars come to the hump for it, those cars must be sent into a temporarily designated xe2x80x9crehumpxe2x80x9d track for reprocessing later. Rehump cars must therefore be handled at least three times before they finally depart the yard.
(e) Since classification tracks are usually too short to make up a whole train, several tracks must be assembled at the trim end of the yard to complete each train. If a train consists of only a single large block, usually that block will have too many cars to fit into a single classification track; it will spill over into additional tracks, thereby reducing the total number of blocks which can be built in the yard.
(f) If more than one switch engine is working on the xe2x80x9ctrimxe2x80x9d end at the same time, movements of these switch engines can interfere with one another, causing unproductive delays and reduction of capacity. Typically, the capacity bottleneck occurs at the xe2x80x9ctrimxe2x80x9d end of the yard rather than at the hump. Then, the heavy financial investment in automated speed control and switching systems at the xe2x80x9chumpxe2x80x9d end of the yard cannot be fully utilized due to the bottleneck at the trim end of the yard. Effective hump capacity can be increased by eliminating this bottleneck at the trim end of the yard, as is proposed by this invention.
(g) All the time cars now spend waiting in the classification yard (typically 12-24 hours) is wasted. Since other cars may be routed into any track at any time (impacting standing cars), it is not safe for mechanical personnel to inspect or repair cars while they lie in the classification yard. Mechanical inspection and repair activities are typically performed in either the receiving or departure yards, adding directly to the total time required to process cars through the terminal. This invention will show how time spent in the classification yard can be effectively utilized in a multiple stage yard.
All known methods of priority based classification rely on traditional single stage sorting. All these techniques have serious drawbacks. Three different methods can be used to classify cars for specific trains:
(a) The most commonly accepted method is to sort cars at the xe2x80x9chumpxe2x80x9d in""the usual way (only by destination block), then select specific cars for each outbound train at the xe2x80x9ctrimxe2x80x9d end of the yard. This is known as xe2x80x9ccherry pickingxe2x80x9d in the railroad industry. In FIG. 6A from O. K. Kwon""s Ph. D. Dissertation (1994) Managing Heterogeneous Traffic on Rail Freight Network Incorporating the Logistics Needs of Market Segments, Dept of Civil and Environmental Engineering, Massachussetts Institute of Technology, pg. 103, the object is to extract a specific car (or group of cars) #1, which are xe2x80x9cburiedxe2x80x9d behind another group of cars #3. Taking group #1 instead of #3 entails extra switching work because it is necessary to first move #1 to another track (FIG. 6B), then put #3 back to the original track (FIG. 6C). This doubles the amount of switching work as compared to only taking xe2x80x9cfirst outxe2x80x9d cars #3.
The advantage of xe2x80x9ccherry pickingxe2x80x9d is to defer decision making until the latest possible time, when the choice of available cars is known for sure; but the method is extremely costly to implement since the xe2x80x9ctrimxe2x80x9d end of the yard is designed for flat switching large blocks of cars, not for sorting by individual car. Digging out priority cars at the trim end of the yard exacerbates the capacity bottleneck which already exists there, and reduces throughput of the whole facility. For these reasons, cherry picking is not considered cost effective by the railroad industry.
(b) A second approach performs all individual car selection at the xe2x80x9chump,xe2x80x9d which is better designed for this kind of work, rather than trying to accomplish it at the trim end of the yard. It can be done by diverting a sufficient number of low priority cars away from their primary classifications into xe2x80x9crehumpxe2x80x9d tracks instead, so that remaining train capacity is just sufficient to take all high priority cars. To implement this, train capacity must be known in advance, which in turn may require determining locomotive assignments well ahead of time. The main disadvantage is that this approach may require committing to decisions up to 12-24 hours prior to the scheduled train departure time. Afterwards, if a planned inbound train does not arrive on time or with all its cars, or if more mechanical defects are discovered than anticipated, it may be hard to get the excess diverted cars back onto the outbound train in time.
(c) To reduce the number of rehump cars, an adaptation of method (b) from Kraft, E. R. (1995) Union Pacific Railroad""s Terminal Priority Movememt Planner, Working Paper, Union Pacific Railroad, Omaha, Nebr., tries to find classification track assignments to start new blocks immediately rather than automatically diverting excess cars into a rehump track. The decision to divert low priority cars is still required as early as before. The approach makes very intensive use of every available inch of classification track space, but also tends to widely scatter blocks for the same outbound train across the entire yard, requiring frequent xe2x80x9ccrossoverxe2x80x9d movements for train assembly at the trim end. Outbound blocks must be trimmed in strict order and absolutely by the scheduled time; otherwise, the whole block to track assignment plan falls apart. The approach relies on very precise adherance to both inbound and outbound train schedules. But even with tight adherance to schedules, there are still distinct advantages to postponing as long as possible a final decision on the exact makeup of the outbound train.
Multiple stage sorting methods have been described by M. W. Siddiquee (1971) in Investigation of Sorting and Train Formation Schemes for a Railroad Hump Yard, in Traffic Flow and Transportation, Proceedings of the Fifth International Symposium on the Theory of Traffic Flow and Transportation, Jun. 16-18, 1971, G. F. Newell, editor, American Elsevier Publishing Company, New York (hereinafter known as Siddiquee, 1971) and by Daganzo, C. F. et al. (1983) Railroad Classification Yard Throughput: The Case of Multistage Triangular Sorting, Transportation Research A, 17A (2) 95-106 (hereinafter known as Daganzo, 1983), as well as by several other authors. No mention of sorting cars by priority has been found in any prior art references on multiple stage sorting. Siddiquee (1971) defines four sorting methodsxe2x80x94by train; by block; geometric and triangular sortingxe2x80x94but these last two are very closely related, and do not constitute significantly different methods for organizing railroad yard operations.
(a) The xe2x80x9cSorting by trainxe2x80x9d method initially collects cars by outbound train, intermixing cars for each train in no particular block order on a single classification track. Those cars are later pulled back to the hump and sorted into specific blocks needed for the train being made up. Finally, blocks must be assembled into proper standing order sequence for departure. This requires a minimum of three handlings per car (including the flat switch at the trim end of the yard) making it noncompetitive with other approaches, unless a special herringbone track arrangment is used (see FIG. 7). By providing intermediate crossover tracks, a herringbone arrangement allows assembly of a train carrying more than one block of cars on a single departure track, without needing to flat switch cars from the trim end of the yard. This reduces the number of car handlings to only two, but a specialized track layout is needed to achieve it.
Technically, cars can be sorted into a herringbone track using only single stage sorting, but construction and maintenance costs of herringbone tracks are so high that carriers generally cannot afford to build a sufficient number of them. If blocks needed for the outbound train are not being built in the herringbone tracks when cars come to the hump, according to N. Miyakawa (1972) in Automation of Koriyama Marshalling Yard and the Herringbone Track. Rail International 1972 (5) 300-320, those cars must be sent into a rehump track instead. To increase utilization of the herringbone tracks, they can be used in the two-stage manner just described. However since Japanese National Railroad did not initially sort by outbound train as suggested here, some rehump cars had to be processed more than twice.
(b) The xe2x80x9cSorting by blockxe2x80x9d method (also called arithmetic or rectangular sorting) intermixes cars of several trains, different blocks of the same train are never intermixed on the same track. As shown in FIG. 8, cars from the first block of each train are intermixed on the first track, cars from the second block of each train are intermixed on the second track; and so on. Just prior to train departure, the cars are resorted by outbound train, simultaneously assembling several trains with all blocks in proper sequence for departure.
Sorting by block inherently requires no more work than conventional single stage sorting, only two handlings per car. However, in a traditional hump yard, classification tracks are usually too short, so several tracks would be required to hold all the cars for each train. Due to this design flaw, outbound trains still need to be assembled in the departure yard by flat switching out of the xe2x80x9ctrimxe2x80x9d end, forcing an unnecessary third handling for each car. This extra handling results entirely from trying to perform multiple stage sorting in a facility not properly designed for it. It also leads to the myth that multiple stage sorting is more costly than conventional single stage processing. To the contrary, the issue is simply one of optimizing facility design to its intended use, but once a yard has been constructedxe2x80x94for better or for worsexe2x80x94this does tend to xe2x80x9clock inxe2x80x9d the operational method for which the facility has been originally designed.
The greatest weakness of sorting by block is the requirement either that all first stage tracks must be completely cleared prior to commencement of second stage sorting (requiring a very long switching lead to hold all the cars from several tracks at once); or that second stage sorting must use different tracks than those used for the first stage sort (as in a xe2x80x9cfoldedxe2x80x9d or xe2x80x9ctwo stagexe2x80x9d design, L. C. Davis (1967) The Folded Two Stage Classification Yard, MBA Thesis, Wharton School, University of Pennsylvania, Philadelphia, Pa., hereinafter known as Davis, 1967). This practically restricts xe2x80x9csorting by blockxe2x80x9d to assembly of only short local trains, or to detailed makeup of trains carrying a very large number of small blocks.
(c) xe2x80x9cGeometricxe2x80x9d and xe2x80x9cTriangularxe2x80x9d sorting are based upon a pattern of arranging blocks which allows intermixing blocks of the same train on the same track; by resorting each track in turn on top of other cars (without requiring all tracks be cleared at once) several trains may be assembled simultaneously in correct block sequence for departure. According to K. J. Pentinga (1959) Teaching Simulaneous Marshalling, The Railway Gazette, May 22, 1959, pp. 590-593, the triangular pattern was adapted from the geometric pattern by the French National Railways (SNCF) so that no car must be sorted more than three timesxe2x80x94but track assignments for the first six blocks are identical (see FIGS. 1 and 2). For more than six blocks, geometric sorting requires slightly fewer tracks, but this savings in tracks is accomplished at the expense of an increase in the total number of cars rehandled. For the purpose of this invention, since very few trains carry more than six blocks at one time, the geometric and triangular patterns will be seen to be practically equivalent.
According to Pentinga (p. 591), the xe2x80x9cGeometricxe2x80x9d sorting pattern is so named because block numbers assigned to each track corresponds to a geometric series of numbers, with a common multiplier of two (e.g. for track 1:1,2,4,8=1xc3x9720, 1xc3x9721, 1xc3x9722, 1xc3x9723; for track 2:3,6,12=3xc3x9720,3xc3x9721, 3xc3x9722; for track 3:5,10=5xc3x9720,5xc3x9721.) Blocks on the first train are numbered 1,2,3, etc. Blocks on the second train are numbered 3,4,5,6, etc. Blocks on the d""th train are numbered 2 (dxe2x88x921)+1, 2 (dxe2x88x921)+2, 2 (dxe2x88x921)+3, etc. Classification track xe2x80x9ckxe2x80x9d is assigned all blocks having the following indices:
bk,j=(2(kxe2x88x921)+1)2(jxe2x88x921)
where bk,j is the j""th lowest block number assigned to track k.
Mathematical equations describing the xe2x80x9cTriangularxe2x80x9d sorting pattern are given by Daganzo (1983, pg. 98, eqn. 8, 9a and 9b). Following Daganzo, blocks on the first train are numbered 1, 2, 3, etc. Blocks on the second train are numbered 2,3,4, etc. Blocks on the d""th train are numbered d (dxe2x88x921)/2+1, d (dxe2x88x921)/2+2, d (dxe2x88x921)/d+3, etc. Classification track xe2x80x9ckxe2x80x9d is assigned all blocks having the following indices:
bk,1=k(kxe2x88x921)/2+1
bk,j=k(kxe2x88x921)/2+jk+1+(jxe2x88x921)(jxe2x88x922)/2, j=2,3,4
where bk,j is the j""th lowest block number assigned to track k. However, a much simpler method of describing the Trangular sorting pattern is shown by Davis (1967, pg. 52, FIGS. 3-7). Davis"" figure is reproduced below as Table 2. To generate the triangular pattern, block numbers are simply arranged left to right, skipping over the position that would normally be used for the second block assignment to each track.
Adopting Siddiquee""s notation, in all drawing figures depicting car movements, parenthesis indicate intermixed groups of cars, but an alphabetic prefix indicating the specific outbound train has been added. For example, (A1 A2 A3) indicates that cars for the first three blocks assigned to train xe2x80x9cAxe2x80x9d, may be randomly intermixed together on the same track. By contrast, (A1) (A2) (A3) indicates that cars for blocks 1,2,3 have been separated into three distinct cuts, following one another in proper standing order on the track and that cars of each block are not intermixed. The notation (A2) (A1) (A3) shows blocks 2, 1 and 3 separated, but not in proper train standing order. These cars would have to be put into proper block sequence either (A1)(A2)(A3) or (A3)(A2)(A1) by flat switching, depending whether the train was intended to depart to the left or right. The first block of any train always follows immediately behind the locomotive, with subsequent blocks in ascending numerical sequence.
For train xe2x80x9cAxe2x80x9d with six blocks, the desired outcome is: (A1)(A2)(A3)(A4)(A5)(A6) for a train departing to the left: this indicates all cars needed for the train have been separated into distinct blocks (cars not intermixed) and all lined up on one track in proper sequence for departure. To simplify""the notation, only one representative car for each block is shown in each example. H. B. Christianson, Should Future Yards Classify Freight in Two Stages? Railway Management Review 72 (2) A20-A32 (hereinafter known as Christianson, 1972) specifically addressed this issue with several examples, demonstrating that the sorting process still works if more than one car is included in each block.
FIGS. 1 and 2 show initial block to track assignment patterns to simultaneously build four trains on four tracks using prior art geometric and triangular sorting, respectively. For easy comparison to past published references, Siddiquee""s block-numbering scheme is used in both figures. In FIG. 1, blocks 1,3,5,7 and 9 for each train are assigned to track 1; blocks 2,6, and 10 are assigned to track 2, block 4 is assigned to track 3, and block 8 is assigned to track 4. Using Siddiquee""s notation, same-numbered blocks for different trains are always assigned to the same tracks; but this can be confusing since the block numbering sequence does not always begin at one for every train. Blocks of train A are numbered 1 thru 10; but train B is numbered 2 thru 10, train C is 4 thru 10, and train D is 8 thru 10.
Such notation would be confusing in later figures, which present continuous sorting patterns. Introducing the notation which will be used throughout the remainder of this application, in FIG. 3A, blocks are renumbered so every train always starts with block #1. Blocks of train B are renumbered 1 thru 9; train C is 1 thru 7 and train D is 1 thru 3. Block to track assignment patterns shown in FIG. 3A and FIG. 2 are actually the same, but FIG. 3A uses the new block numbering sequence, which is used in the remainder of this application.
FIGS. 3B thru 3E work through a complete sequence of switching cars using the prior art triangular sorting method. This prior art pattern assembles all four trains simultaneously, so these trains should all be scheduled to depart close to the same time. A detailed step-by-step explanation of the sorting process follows. In later figures, including ones showing continuous sorting processes, each track is similarly sorted in turn and each drawing figure shows the result after the completion of each sorting step. A textual description is only provided (below) tracing the steps of FIGS. 3A-3E, but for every series of drawing figures depicting car movements, a table is provided summarizing the sequence of car movements needed to carry out the sorting process. For ease of comparison, each table is numbered the same as the set of drawing figures to which it relates, even though in some cases this results in tables being shown here out of numerical order. For example, Table 3 below describes the sequence of railcar movements shown in drawing FIGS. 3A-3E.
The initial yard setup is shown in FIG. 3A. This configuration of block to track assignments would be maintained for most of the day (perhaps 20 hours) while arriving inbound trains are processed, and cars for all four trains are collected in the classification tracks.
When departure time approaches, outbound train assembly is started by retrieving the contents of Track #1 and pulling those cars back to the hump. These cars are reswitched as follows: A1 to Track 1 by themselves, A3 and B2 to track 2, on top of cars already there; A5, B4 and C2 to track 3, on top of cars already there; and A8, B7, C5 and D2 to track 4. The result, shown in FIG. 3B has cars for block (A1) isolated by themselves on track 1, while cars on the other three tracks are segregated into two distinct groups of blocks, and cars are not intermixed between distinct groups.
Next, track 2 is retrieved. The entire track is pulled back to the hump, including all cars just sent in from reprocessing of the first track. These cars are routed as follows: A2 and A3 to Track 1, B1 and B2 to Track 2, A6, B5 and C3 to Track 3, and A9, B8, C6 and D3 to Track 4. The result, shown in FIG. 3C has (A1) (A2) (A3) assembled in proper order on track 1; since blocks (A2) and (A3) were not intermixed on track 2, they will not be intermixed when those cars are collected on track 1; and train B is started on track 2. Cars on the other two tracks are segregated into three distinct groups of blocks, whereby cars are not intermixed between groups.
Track 3 is then reprocessed in a similar fashion. As shown in FIG. 3D, cars on track 4 are segregated into four distinct groups of blocks. By reprocessing this last track, all four trains are simultaneously assembled in proper standing order, without requiring use of more than four tracks at any time. The final result is shown in FIG. 3E.
Note that a six block train could be built using a block to track assignment pattern for seven (or more) blocks, simply by assuming that some blocks have no cars. This is shown in FIGS. 9A thru 9D, where the position normally reserved for the third block has no cars, so subscripts 4-7 have been resequenced as 3-6, respectively. Table 9 below describes the sequence of railcar movements shown in drawing FIGS. 9A-9D. Thus, the geometric pattern could be derived from the triangular pattern, and vice versa, simply by skipping some intermediate block positions. For the purpose of this invention these two patterns are treated as, in fact, equivalent as well as any variations which can be constructed by simply skipping intermediate block positions.
Another improvement results from simply taking advantage of triangular sorting""s capability to build trains in proper block standing order. In triangular sorting, cars assigned to a xe2x80x9chead blockxe2x80x9d slot (the first block in standing order sequence on each track) are handled twice, whereas other cars must be handled three times. Therefore, Daganzo (1983) suggests blocks with the largest number of cars should be assigned to xe2x80x9chead blockxe2x80x9d slots to minimize the number of cars rehumped. But if that is done, the order of the blocks must be rearranged by flat switching before the outbound train can depart. Doing this might make sense in a traditionally designed yard where cars must be trimmed out anywayxe2x80x94but clearly in a new facility the benefit of completely eliminating the trim operation would outweigh the cost of rehumping a few additional cars, given that the basic design of a multi stage sorting facility must provide for a very high capacity hump and an effective car speed control system. Although the extension to sequence blocks strictly in the order required by the transportation plan may seem obvious, prior literature teaches against the practice.
A number of prior art citations are furnished with this Patent application which are not otherwise discussed in the specification. This section provides a brief discussion of each of those citations. It is hoped that future researchers may benefit by having a comprehesive survey of prior literature in multiple stage switching techniques.
Herbert T. Landow published a series of two articles, as Overseas Railroads Try New Yard Techniques (Part I), pp 95-100, and Train Blocks and Herringbones (Part II), pp 101-102, both in September 1968 Modern Railroads. The first article discusses several means of car retardation and car mover devices and how these can be used to improve yard efficiency, but Part I does not discuss multiple stage switching techniques. Part II describes herringbone track layouts (as shown in FIG. 7) and prior art geometrical and triangular switching techniques. A third article by Landow, in Yard Switching with, Multiple Pass Logic, Railway Management Review, Vol. 72 No. 1, pp :11-23 uses difficult notation which is hard to follow. However Landow""s context (p 16) is that xe2x80x9cSimultaneous switching is applicable in any case where two or more trains are to be sent out of a yard at or near the same time.xe2x80x9d This restriction is clearly associated with the prior art method of batch sorting of trains. None of these papers address either the continuous approach to multiple stage sorting, as this invention does, nor do they discuss the ability to use multiple stage sorting to preselect particular cars if an outbound train exceeds capacity.
Hoppe, C. W. (1972) in Do We Need Yards? Railway Management Review, Vol 72 No. 2 pp A1-A6 discusses general problems associated with prior art designs for railroad classification yards. Hoppe""s article has a very short section on multiple stage switching techniques concluding (p A5) xe2x80x9cIt does little good to design a yard with great potential if the men who are going to run it are not trained to run it.xe2x80x9d Christianson (1972), as cited previously, examines several real-world yard configurations, finally concluding, xe2x80x9cno large two-stage yard operation exists anywhere in the world.xe2x80x9d A later article by Christianson, H. B., et al (1979) in Committee 14xe2x80x94Yards and Terminals, Report on Assignment 7, Yard System Design for Two Stage Switching, American Railway Engineering Association, Proceedings 79""th Annual Conference, Vol 81, pp 145-155, repeats much of the material from Christianson""s 1972 article but concludes xe2x80x9cOne alleged disadvantage is that personnel cannot learn and effectively use two-stage switching, but a seven-day test at a large flat yard and a two-day experiment at a medium-sized hump yard refuted this. Two staging will work in a normal environment with normal delays and problems.xe2x80x9cNeither of Christianson""s papers offer any improvement to the basic techniques of two stage switching, as this patent application does.
Rao, M. S. (1976) in Switch Back Humpxe2x80x94A New Marshalling Tool, Rail International 1976, No. 4, pp 219-222 proposes to use a steep gradient to cause cars actually to reverse direction and then be routed into a secondary sorting yard. Rao proposes to utilize multiple stage switching techniques to maximize the productivity of his switch back hump. The novel aspect of Rao""s paper is the reversal of direction which cars undergo during the humping process; however Rao offers no improvements to prior art multiple stage switching techniques. Rao""s paper also appears as a prior art citation in U.S. Pat. No. 4,766,815 to Chongben et al (1988). Chongben proposes using a section of ascending gradient only to reduce car speeds rather than to actually reverse the cars"" direction, as Rao does. Chongben""s patent does not address multiple stage switching but only the design of the car retarder systems in the yard.
Middleton, W. D. (1979) in New Approaches to Yard Automation in Japan, Railway Age, Feb. 12, 1979, pp. 46-49, does not discuss multiple stage switching techniques, but this citation is provided as a further reference on the Japanese National Railroad""s use of Herringbone tracks and car retarder systems. Koehn, K., Holt, H. L. and Sabeti, A. (1972) in European Yard Retarder Systems, Railway Management Review, Vol 72 No. 2 pp A7-A19 offer a survey of many different kinds of car retarder systems, which provide an alternative to the traditional xe2x80x9cclaspxe2x80x9d retarder systems (as in U.S. Pat. No. 5,388,525 to Bodkin, 1993) now widely used in the United States.
Welty, G. (1980) in Outlook: Fewer Yards, Faster Output, Railway Age, Oct. 13, 1980, pp. 16-17, surveys the then-current state of the art in railroad classification yard technology. He states, xe2x80x9cFirst, discard the radical. Linear-designed yards may work overseas, but experts who have looked at these and other nonstandard yards say that they simply don""t meet the requirements of railroading in North America Thus, the new classification yards of tomorrow, like those of today and yesterday, will have the standard componentsxe2x80x94receiving yard, class yard, and departure yard, either inline or wraparound, depending mostly upon the constraints of available space.xe2x80x9d This teaches against the current invention. The ability to successfully implement xe2x80x9cnon standardxe2x80x9d yards in North America was later reported by Welty in At Livonia, An Early Payoff, Railway Age, February 1995, pp 41-42, describing a successful application of the xe2x80x9cDowtyxe2x80x9d retarder system at Union Pacific""s yard at Livonia, La., one of the very few new classification yards constructed anywhere in North America during the 1990""s.
Kraft, E. R. and Guignard-Spielberg, M. (1993) in A Mixed Integer Optimization Model to Improve Freight Car Classification in Railroad Yards, Report 93-06-06, Department of Operations and Information Management, The Wharton School, University of Pennsylvania, propose to simultaneously optimize both hump sequence and dynamic block to track assignments using a network-based, mixed integer math programming formulation. Using a decomposition approach, Wang, X. (1998) in Improving Planning for Railroad Yard, Forestry and Distribution, Ph. D. Dissertation, Department of Operations and Information Management, The Wharton School, University of Pennsylvania, was able to scale up Kraft and Spielberg""s approach to solve a realistically sized problem within a reasonable time frame. However, Kraft""s formulation was only tested using a xe2x80x9ctoyxe2x80x9d problem of 3 trains, 4 time periods, 3 blocks and 2 tracks, not practical for any real applications. In order to solve the problem, Wang adjusted some constraints so that they may no longer represent a feasible solution to Kraft and Spielberg""s original problem. Both the Kraft and Spielberg (1993) and Wang (1998) formulations attempt to preselect cars for specific outbound trains; but both rely on single stage sorting techniques in traditional hump yard facilities; they do not use any multiple stage sorting techniques as advocated by this invention.
In accordance with the present invention, outbound trains are built in proper standing order for departure directly from the classification tracks, using a continuously sustainable multi-stage sorting process. During this process, cars are easily separated based on priority or according to their delivery time commitments, so connections of cars needing to go on a specific train can be protected. During second stage sorting operations, cars may be inspected or repaired while they await outbound connections in the classification tracks, effectively utilizing otherwise idle time and resulting in considerable savings in time required to pass through the yard. This may be accomplished in a traditional rail yard setting, but will yield even more benefit if accomplished in one of the specialized facility designs shown in the drawing figures.
Accordingly, several objects and advantages of the present invention are:
(a) The continuous multiple stage sorting process utilizes terminal resources more uniformly and thus efficiently than prior art methods.
(b) If more cars are available than the capacity of the outbound train, the decision which specific cars to take is not required until immediately before train departure, rather than 12-24 hours in advance as with some prior art single stage sorting methods.
(c) Tracks can be used for more than one purpose, allowing flexible use of assets and eliminating unnecessary movement of cars within the yard. Single car sorting is efficiently performed at the hump. Preblocked groups of cars may be conveniently transferred from one train to another by flat switching at the opposite end of the yardxe2x80x94without requiring preblocked cars to be unnecessarily reprocessed over the hump or moved a long distance in a special flat switching transfer, as current yard designs do.
(d) Yard designs proposed here, particularly the preferred embodiment, utilize a very simple track layout, offering a distinct possibility that new yards could be constructed to an essentially standardized design, with only minor variations such as the exact length and number of tracks needed in each yard. Computer software needed for both yard design and process control can be standardized across many facilities, rather than having to be heavily customized for each individual yard. The guesswork can be eliminated from yard design by utilizing such standardized computer simulation tools to ensure facilities are properly sized.
(e) Assembly of outbound trains by flat switching at the trim end of the yardxe2x80x94and the related capacity bottleneckxe2x80x94are completely eliminated. One additional hump operation is required to replace the flat switching which now occurs at the trim end of the yard. However, this poses no inherent difficulty provided the hump is designed with sufficient capacity to accomplish its intended workload. Since the hump operation should actually proceed faster than the trim operation it replaces, the net effect should be a savings in operating cost per car classified, as well as in the capital construction and maintenance costs of the yard facilities themselves.
(f) The total number and aggregate length of tracks needed in the yard is considerably reduced. The need for separate receiving and departure yards is eliminated altogether. In the classification yard, instead of many short tracks (for example, 60 tracks up to 40 cars long), only a few long tracks must be built (for example, 15 tracks up to 150 cars long.) Fewer tracks need fewer switches and retarder units (for controlling car speeds) to construct and maintain. Compared to conventional hump yard designs, proposed new multi-stage yards will be considerably more economical to construct, maintain and operate.
(g) With fewer classification tracks, a relatively straight path can be constructed from the hump into any of the tracks, and the distance is reduced from the hump to the clearance point of the farthest classification track. This improved geometry raises the probability a car will at least roll clear of the switching area, thereby increasing the capacity and throughput of the humping operation. Many multiple car cuts are humped, especially during second stage sorting. Hydraulic car retarders, well known as xe2x80x9cDowtyxe2x80x9d unitsxe2x80x94see A. W. Melhuish (1983) Developments in the Application of the Dowty Continuous-Control Method, Transportation Research Record 927 pp. 32-38 (hereinafter Melhuish, 1983); D. E. Bick (1984) A History of the Dowty Marshalling Yard Wagon Control System, Proceedings of the Institute of Mechanical Engineers 198B (2) 19-26 (hereinafter Bick, 1984); and U.S. Pat. No. 5,092,248 to Parry (1992)xe2x80x94are well suited to accomodate the requirement for processing multiple car cuts, and this retarder system can provide continuous speed control for very long classification tracks as well. As compared to conventional single stage hump yardsxe2x80x94where cars are nearly always sorted one-at-a-time and where the humping process is subject to frequent interruptionsxe2x80x94excellent geometry and frequent processing of cars in multiple car groups should substantially increase the hump processing rate. Another benefit of the Dowty retarder system is practical elimination of lading and railcar damage by preventing overspeed coupling impacts in yards.
(h) Inspection and servicing of cars while they wait for connections on classification tracks may save perhaps 5-10 hours in the average time required to process cars through the yard. This practice also permits more efficient utilization of mechanical forces by allowing their activities to be spread uniformly throughout the day, rather than unduly determining maintenance personnel needs based on (often highly peaked) train arrival and departure patterns.
(i) FIG. 4 shows the potential to bypass intermediate terminal handlings, by improving sorting capabilities at railyards which originate and terminate a sufficient volume of local traffic (in the vicinity of 1000 cars per day total). Currently, such yards often have only xe2x80x9cflatxe2x80x9d switching capability, so it is more efficient to send cars to a nearby xe2x80x9chumpxe2x80x9d yard for detailed individual car classification. By converting from flat switching to a multiple stage hump yard design, as proposed here, cars may be economically sorted at the originating yard, allowing more trains to be operated on a direct xe2x80x9cpoint to pointxe2x80x9d basis, rather than continuing the industry""s current over reliance on a xe2x80x9chub and spokexe2x80x9d network design.
Still further objects and advantages will become apparent from consideration of the ensuing description and drawings.